What’s up with those ‘friendly skies?’

But nothing I’ve experienced myself or heard about tops what happened to the 69-year-old Vietnamese-American doctor who boarded a United Airlines plane in Chicago last Sunday and was forcibly dragged off and injured.

Each time I write anything critical of the commercial aviation industry, a jet stream of complaints results (mostly from local employees of it), who talk about how great and flawless the big airlines are — when we all know different.

Granted, commercial aviation generally carries on a valuable service day in and day out, in terms of both safety records and efficient transport of people from points A to B all around the globe thousands of times without incident. Publicity from the relatively few crashes that do occur greatly obscures what the industry quietly accomplishes on a regular basis.

This being said, nothing is perfect. And I sometimes get the impression that when atrocities do happen, such as passengers being stranded on a runway or waiting in security lines for hours at a time, the airline industry’s first impulse is to blame everyone besides itself.

Those long-suffering passengers not only pay huge sums to fly someplace, they are expected to arrive at the gate well in advance of departure times just to undergo the indignity of a Transportation Security Administration checkpoint.

Passengers must know what they may bring aboard an aircraft and otherwise tow the mark.

Yet if a flight is delayed or some other issue occurs through no fault of their own, passengers are expected to sit there and not make a peep. And if he or she does complain and respond in a manner that can be considered disruptive in any way, a harsh security response is triggered.

The airline industry operates much like a totalitarian government bullying its citizens. Whereas some business enterprises have a philosophy that the customer is always right, the customer is always wrong when he or she butts heads with an airline.

Well, similar to a sky of azure blue, a pleasant sight is on the horizon which unfortunately has arisen from the equally ugly event in which Dr. David Dao was victimized last Sunday — and thankfully preserved for posterity due to the miracle of video.

While what happened to him is certainly a tragedy, it could be THE case that once and for all forces the airline industry to finally begin treating passengers with the respect they’re owed.

Dao had bought his ticket in good faith for a flight from O’Hare International Airport in Chicago to Louisville, Kentucky.

The problem occurred due to airlines’ policy of overbooking flights, to ensure they will be transporting an optimum number of people. The idea is to fill any empty seats that no-show passengers leave behind.

Obviously, there are cases in which everyone shows up as scheduled, and push literally comes to shove and people are “bumped” — or denied seats on a flight even if they have confirmed reservations. In such cases, the airlines usually provide compensation to bumpees such as hotel stays, meal coupons and flight vouchers.

That can be well and good, except for the person who needs to get somewhere fast.

Dao was offered $800 by United to give up his seat, which he declined — and in response was dragged from the plane by Chicago aviation police to make room for four crew members on the flight.

During the ordeal, he suffered a concussion, broken nose and lost two front teeth and was hospitalized for three days. Dao also will need reconstructive surgery. His appearance afterward resembled a war casualty, and the poor guy remarked that being dragged down the plane aisle indeed was more terrifying than his experience fleeing Vietnam in 1975.

Remember, this involved United Airlines, which launched its famous “Fly the friendly skies” advertising slogan and catchy theme song 10 years earlier, in 1965.

Predictably, Sunday’s incident has gone viral, making United the object of worldwide outrage with boycotts and other reactions — justly deserved.

No doubt it will end up paying a seven-figure lawsuit settlement to Dr. Dao as well as suffering a public-relations nightmare in the highly competitive air-transportation arena.

Of course, the goal at this point is damage control, but I wonder if the debacle is causing United and other airlines to examine its root cause: an inherent systemic mistreatment of passengers.

Dr. Dao’s only “crime” was resisting authority, which had no right to exercise it in such a manner in the first place.